1. Field of the Invention
The present invention relates to a data storage device, and more particularly, to a disk drive including voice coil motor magnet plates formed integrally with the base and/or cover of the disk drive during the drive fabrication process.
2. Description of the Related Art
In general, Winchester-type disk drives operate by transferring data between read/write transducing heads and respective data tracks on magnetic storage disks. The transducing heads are supported by an actuator assembly, which is provided to pivot the heads across the surfaces of the disks. Pivoting of the actuator assembly and transducing heads is generally accomplished by a voice coil motor ("VCM") provided as part of the actuator assembly at an end of the actuator assembly opposite the transducing heads.
A VCM is typically comprised of a permanent magnet stationarily mounted within the drive, and electrical windings fixedly mounted to the actuator assembly, adjacent to the magnet, so as to pivot with the actuator assembly. The windings are located within a magnetic field set up by the magnet, and, upon introduction of an electric current through the windings, the magnetic field will exert a force on the windings causing the actuator assembly and transducing heads to pivot. The VCM is coupled to control electronics, which control the current through the windings, and thus control the positioning of the actuator assembly and transducing heads with respect to the storage disk.
The time it takes to pivot the actuator assembly so as to move the transducing heads between different data tracks on the storage disk in response to control signals is referred to as the drive seek time. With past improvements to disk drive microprocessors, the seek time of a disk drive has become the major factor limiting the rate at which data is transferred between the heads and disks. As such, there has been an industry wide effort to minimize seek time. Seek time is primarily dependent on the torque which can be generated in the VCM to pivot the actuator assembly between data tracks on the disk. Several factors effect the maximum VCM torque, including the strength of the magnetic field, the moment of inertia of the actuator assembly, and the inductance of the electrical windings. In the case of inductance, a high inductance within the windings of the VCM will result in a high resistance to a change in the current within windings. As a quick change in current is necessary for fast seek times, a high inductance within the windings will result in slower seek times.
Conventionally, the voice coil magnet assembly also include magnetically permeable plates adjacent to the magnet, which plates are fixedly mounted within the drive housing. Conventional magnet assemblies have further included magnetically permeable return posts extending between the top and bottom magnet plates. The magnet plates and the return posts together provide a closed magnetic field loop for the magnetic flux lines emanating from the permanent magnet. This configuration was provided to maximize the magnetic field in the vicinity of the actuator's windings. The magnetic field in this region contributes most directly to the strength of the torque generated by the VCM.
The provision of return posts within the VCM creates certain disadvantages, but the posts have heretofore been necessary in order to provide the requisite magnetic field intensity. One such disadvantage is that the presence of the return posts within the VCM increases the inductance within the windings. As previously stated, increased inductance results in slower seek times. Another disadvantage presented by the return posts is that the posts are manufactured with engineering tolerances and no two posts are of exactly the same construction. Posts of even slightly different sizes and/or constructions will vary the magnetic field travelling through the closed loop. Thus, the magnetic field between the magnets, and consequently the torque created by the VCM, will vary in different disk drives. Further still, providing side posts adds to the complexity and cost of manufacturing the disk drive.